TY - JOUR
T1 - Cluster analysis successfully identifies clinically meaningful knee valgus moment patterns: Frequency of early peaks reflects sex-specific ACL injury incidence
JF - medRxiv
DO - 10.1101/19001511
SP - 19001511
AU - Sigurðsson, Haraldur Björn
AU - Bríem, Kristin
Y1 - 2019/01/01
UR - http://medrxiv.org/content/early/2019/07/08/19001511.abstract
N2 - Background: Biomechanical studies of ACL injury risk factors report heterogenous results, analyze only a fraction of the data, and do not analyze data in accordance with the injury mechanism. Extracting a peak value of relevance to ACL injuries is challenging due to differences in the relative timing of the peak value. Aims/Hypotheses: The aim was to cluster analyze the knee valgus moment time series curve shape in the early stance phase. We hypothesized that 1a) There would be few discrete curve shapes, 1b) there would be an early peak pattern, 2a) youth athletes of both sexes would show similar frequencies of early peaks, 2b) adolescent girls would have higher early peak frequencies. Methods: N=213 (39% boys) youth soccer and team handball athletes (phase 1) and N=35 (45% boys) with 5 year follow-up data (phase 2) were recorded performing a change of direction task with 3D motion analysis and a force plate. The time series of the first 30% of stance phase were cluster analyzed based on Euclidean distances in two steps; shape-based main clusters with a transformed time series, and magnitude based sub-clusters with body weight normalized time series. Group differences (sex, phase) in curve shape frequencies, and shape-magnitude frequencies were tested with chi-squared test. Results: 6 discrete shape-clusters and 14 magnitude based sub-clusters were formed. Phase 1 boys had higher frequencies of early peaks than phase 1 girls (38% vs 25% respectively, P&lt;0.001 for full test). Phase 2 girls had higher frequencies of early peaks than phase 2 boys (42% vs 21% respectively, P&lt;0.001 for full test). Conclusions: Cluster analysis can reveal different patterns of curve shapes in biomechanical data. The early peak shape is relatable to the ACL injury mechanism as the timing of its peak moment is consistent with the timing of injury. Higher frequency of early peaks demonstrated by Phase 2 girls is consistent with their higher incidence of ACL injury.Competing Interest StatementThe authors have declared no competing interest.Funding StatementFunding for the study was provided by The Icelandic Centre for Research (Rann?s ? Rannis.is), funding codes 120410021, 903271305, 1203250031, and 185359051. The Football Association of Iceland has provided travel funds to the lead author to present findings at a conference. No funding source was involved in the study design, the execution of the study, the data analysis, writing the report, the decision to publish the results, or writing the article.Author DeclarationsAll relevant ethical guidelines have been followed and any necessary IRB and/or ethics committee approvals have been obtained.YesAll necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived.YesAny clinical trials involved have been registered with an ICMJE-approved registry such as ClinicalTrials.gov and the trial ID is included in the manuscript.NAI have followed all appropriate research reporting guidelines and uploaded the relevant Equator, ICMJE or other checklist(s) as supplementary files, if applicable.YesA number of decisions have to be made by the authors during data processing and analysis. The field of cluster analysis has not reached consensus on how to select many important parameters during the cluster analysis process, including the number of clusters. In order to facilitate replication and auditing of the results presented, a data set that can be used to replicate the cluster analysis will be uploaded at datadryad.org should the manuscript be accepted. The data set includes the R code used to perform the cluster analysis. The data is uploaded as additional documents for submission in JEO.
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